Lect 5: Fluids & Solids Flashcards by Taylor Walker

matter that is either liquid or gas; molecules bond weakly, break, and reform because of higher Kinetic Energy; create permanent Forces outward (Normal to the surface); Permanent force withstands the Force parallel to the surface; Matches shape of container; Gravitational Force causes flat top in liquids

Fluid

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property of fluids that can be externally viewed and measured; Quantity can change
Ex: mass and Energy

extensive properties of fluids

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properties of fluids that are intrinsic; Independent of quantity;
Ex: density, pressure

Intensive

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the “heaviness of a fluid”; the mass in a specific volume; changing the amount of the fluid does NOT change this; this is changed only by a change in volume without a change in mass; Solid measurement SI unit = kg / m^3;

density (rho)

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Equation: Density

Density (rho) = m / v

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the density of a subject compared to the density of water; ratio quantity

specific gravity

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If the density (specific gravity) of the substance is less than 1, the substance is _____ than water

lighter

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if the density (specific gravity) of a substance is greater than 1, the substance is _______ than water

heavier

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Equation: Specific gravity

Specific Gravity = density (substance) / density (water)

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Specific gravity / density of water

1000 kg / cm^3

1 g / cm^3

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a Force per unit area; SI unit = Pascals (Pa)

Note: also “stored” energy per unit area

pressure

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results from impulse (change in momentum) or F(collision) * time of molecular collisions; change in momentum is the average number of collisions / time of collisions and the surface area of the object in the collisions; SI unit = Pascals (Pa)

fluid pressure

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Equation: Pressure

P = F / A

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a fluid at rest only experiences a force ______ to the surface

perpendicular

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pressure of a disc submerged in water

P = weight (m*g) of fluid ABOVE the disc / area of the disc

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Pressure is ______ of the area chosen

independent

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Equation: Pressure of a Fluid at rest in a sealed container w/ uniform density

P = (density, rho) * g * y
Note:
y = depth of the fluid
g = gravitational constant

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Equation: Pressure of a fluid at rest in an open container

P = density (rho) * g * y + P(atm)

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Pressure of the atmosphere

101,000 Pascals

1 atm

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Pressure of a fluid ______ as y (depth of fluid) goes down. Why?

decreases; bc there are fewer molecules above the object causing less weight

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The pressure compared to local atmospheric pressure;

Gauge pressure

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“Negative” pressure

always refers to gauge pressure; Pressure for the system is less than that in the atmosphere

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pressure measured relative to a vacuum as 0

absolute pressure

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Equation: Absolute pressure

P(abs) = P(g) + P(atm)

NOTE: P(g) is Gauge pressure

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Each point in an enclosed fluid must bear any increase in pressure pressure applied anywhere to an enclosed incompressible fluid will be distributed undiminished throughout that fluid

Pascal's Principle

a simple machine that works via Pascal's Principle; Force on Piston 1 applies pressure on incompressible fluid; All pressure is transferred to Piston 2 (w/ a larger Area)--Force is proportionately greater but acts over a larger distance So, ∆P1 = ∆P2

hydraulic lift

an ideal machine does not change ______

Work

the upward force acting on a submerged object; Displaces volume due to a difference in pressure equal to the weight (m*g) of the fluid displaced

Buoyant force: F(b)

Equation: Buoyant force

density (rho) of the fluid * V(g) | Note: V(g) = volume displaced

Equation: Floating Object

submerged part of the object = density of the object / density of the fluid Note: If floating in water, the ratio = specific gravity of that object

motion in a fluid at rest | contributes to the fluid pressure

random translational motion

motion that is shared equally by all molecules at a point in the fluid; motion of the fluid as a whole; does not contribute to fluid pressure

uniform translational motion

Equation: Velocity of fluid coming from a spigot

V = √2*g*h

a fluid with no viscosity that is incompressible, no turbulence, irrotational flow

ideal fluid

measure of a fluid's resistance to Force that is not perpendicular to the surface; fluid's tendency to resist flow Ex: syrup > water

viscosity

fluid w/ uniform density | *Assume this for MCAT

incompressible fluid

steady flow of a fluid; all fluid flowes through a fixed point will have the same VELOCITY

Laminar flow

Equation: Continuity equation (Volume flow rate)

Q = A * v | Note: Q = volume flow rate

rate at which a volume of liquid moves through a pipe

volume flow rate (Q)

equals a fluid's volume flow rate * density

mass flow rate (I)

Equation: Mass flow rate (I)

I = density (rho) * Q = density (rho) * A * v

For an Ideal fluid, the ______ is constant, and Area and Volume are ______ related

``` Flow rate is constant inversely related (narrow pipe = high velocity) ```

Equation: Bernoulli's Equation

P + density (rho) * g * h + 1/2 * density (rho) * v^2 = K | Note: K = constant specific to a fluid in a given situation of flow; h = distance ABOVE some arbitrary point

given one continuous idea flow; sum of its three terms is a CONSTANT at any point in the fluid similar to conservation of energy: dividing any term by Volume gives units of energy

Bernoulli's equation

Equation: gravitational potential energy per unit volume of a fluid

m * g * h / V | Note: Second term in Bernoulli's equation

Equation: kinetic energy from the uniform translational motion of the molecules in a fluid per unit volume

(1/2 * m * v^2) / V | Note: third term in Bernoulli's equation

Equation: Energy per volume from the random motion of the molecules in a fluid

P / V | Note: First term from Bernoulli's equation

Uniform translational energy borrows energy from _____________. Pressure goes down

Random translational kinetic energy

Pressure and velocity are ________ related in ideal fluids

inversely; As velocity goes down, pressure goes up

predicts deviation from ideal fluids; Ex: drag

Non-ideal (Real) fluids

occurs at the fluid - object interface most often; force is working against the flow

drag

the intensity of the intermolecular forces per unit length in a fluid temperature dependent depends on which type of fluid is interfacing

surface tension

the force on a fluid causes water droplets by maximizing the surface area

intermolecular forces

allows a fluid to be pulled up a thin tube

capillary action

intermolecular force that causes surface tension

cohesive force

force between molecules of the tube and the fluid molecules

adhesive force

type of matter in which atoms and molecules are held together rigidly; molecules change dimensions by stretching / compressing but not breaking

solids

force applied to a solid object / Area over which the Force is acting i.e. What is done to an object

stress

Equation: Stress

Stress = F / A | SI Unit = N / m^2

the fractional change in an object's shape | i.e. how an object responds

strain

Equation: Strain

strain = ∆dimension / original dimension

the maximum stress point an object can take; beyond this point, the object loses its original shape

yield point

when stress exceeds the yield point for an object

Fracture point

3 Stress modules for solids

young's module (E) - tensile strength shear's module (G) - shear stress Bulk module (B) - compression / expansion

Equation: Young's module

E = (F/A) / (∆h /ho)

Equation: Shear's module

G = (F/A) / (∆x / ho)

Equation: Bulk module

B = ∆P / (∆v / vo)

Solids ______ when heated due to more molecular vibrations. May be either linear or volume

Expand

Equation: Modulus of elasticity

Modulus of Elasticity = Stress / Strain